Magnetic disk apparatus are now indispensable as main storage devices for information related apparatus such as computers and so on, and a higher capacity and faster recording/reproducing are increasingly required therefor as the need for faster processing of a huge amount of data arises for images and audio. For this purpose, faster read/write operations as well as a higher recording density are required. It is essential, as to the recording density, to reduce as much as possible the substantial distance from an element of a recording/reproducing head to a recording film of a magnetic disk serving as a recording medium, and to reduce a track width, and as to the faster operations, to increase the speed of data processing, rotational speed, and seek speed. With these improvements, a magnetic head, which has conventionally operated with a sufficient spacing from a magnetic disk, is forced to operate in a so-called intermittent contact state in which the magnetic head operates nearly in contact with the magnetic disk at a high speed. In addition, for reducing the substantial distance between a magnetic head element and a recording film of a magnetic disk as mentioned above, it is necessary to make a protective layer and a lubricant layer, intervening therebetween, as thin as possible. Specifically, the protective layer should be 10 nm or less; the lubricant layer should be 2 nm or less; and an average spacing between the disk surface and the head should be 30 nm or less, where a contact could occur as the case may be. To realize a magnetic disk which is fit for practical use in such extremely tight conditions, it goes without saying that a key point lies in how to design materials and shapes for the protective layer, the lubricant layer, and a contact portion of the head.
The protective layer and the lubricant layer of the magnetic disk have been conventionally improved from a viewpoint of an increase in abrasion resistance, sliding resistance, corrosion resistance, and soon. The protective layer has been practically made of an amorphous carbon film formed by sputtering graphite in an Ar atmosphere, amorphous hydrogenated carbon film formed likewise by sputtering graphite in an Ar+H2 or Ar+CH4 atmosphere, and so on. In addition to those, a variety of protective films have been under consideration such as those made of diamond-like carbon formed by plasma CVD with a hydrocarbon gas, a carbon film containing a variety of additive elements such as Si, Ti, W, Fe and so on, BN, SiO2, and so forth. Further, JP-A-62-287415 discloses an example which employs a laminate of two types of carbon layers having different hardness, and a soft underlying layer as a buffer layer, particularly with the object of improving a mechanical strength. JP-A-9-91687 also discloses an example which has a protective film having a hardness varying in a film thickness direction. However, either of them is not fit for practical use due to insufficient strength or corrosion resistance when an extremely thin film of 10 nm or less in thickness is concerned.
In respect to the lubricant layer, on the other hand, perfluoropolyether based lubricating oils having absorptive functional groups at terminals are typically used, and a number of lubricants having terminal groups exhibiting an improved integrity with a protective layer have been disclosed.
In conventional use environments, however, considerations on the protective layer and the lubricant layer only have to be made for sliding with a head upon starting and stopping a disk apparatus, i.e., a so-called contact start stop. In actual read and write operations, no problem associated with sliding arises, since the head is spaced from the disk, except for introduction of foreign substances therebetween.
In contrast, a high recording density magnetic disk apparatus for high speed processing, addressed by the present invention, is highly damageable to a contact of a head with a disk rotating at a high speed, or interactions of the two through an air flow or the like, if not contacting, causing damages on a protective layer and resulting damages on the disk itself, so that a need exists for a protective layer which possesses in combination different performance from conventional ones. Thus, any of the above cited techniques is not fit for practical use in an disk apparatus which requires low flotation and extremely thin films, as intended by the present inventors.
It is an object of the present invention to provide a magnetic recording medium which exhibits less damages and a high durability in high speed low flotation sliding, and a highly reliable magnetic storage apparatus by realizing a magnetic recording medium having an extremely thin protective layer having a substantial thickness of 10 nm or less, which can even be used in such severe conditions.